The objectives of the proposed research are to elucidate the effect of specific intervention on myocardial contractile force, oxygen consumption, and energy conservation during ischemia produced by coronary occlusion and during recovery from ischemia following re-establishment of coronary flow. Interventions will include perfusion of the myocardium with various purine nucleosides and nucleobases. In intact dog heart preparations, left ventricular contractile force will be monitored using Walton-Brodie strain gauge arches and left ventricular oxygen consumption will be monitored by measuring left coronary flow and A-V oxygen difference. Ischemia will be produced by occluding inflow, and the effect of intraventions on contractile force and oxygen consumption will be evaluated both during ischemia and during recovery. In separate experiments, the effects of these interventions on high energy phosphate levels during ischemia and recovery will be estimated. In these studies, localized ischemia will be produced so that the effects of the interventions on ischemic muscle as well as adjacent nonischemic muscle may be studied.